You may be aware that the USA was one of the first countries to legislate on global tax evasion and avoidance. This is now supported by governments around the World. FATCA aims to identify and report specified 'US persons' responsible for paying US tax, who hold accounts and/or investments outside the US.
It requires foreign financial institutions (i.e. those outside of the USA), such as NatWest International, to identify and report this information to the local tax authority, who in turn will report to the US Internal Revenue Service (IRS). Numerous countries around the world have entered into agreements with the US, and passed local legislation to enable and mandate compliance with FATCA.